Work, Energy and Momentum Flashcards
What is the spring constant of a spring?
The force per unit extension needed to stretch it
What happens if a spring is stretched beyond its limit of proportionality?
It no longer obeys Hooke’s law
What is Hooke’s law?
Force applied = spring constant x extension
Explain what Hooke’s law means?
That the extension of a spring is directly propionate to the force applied to it
provided the limit of proportionality is not exceeded
What is elastic potential energy?
Energy that is stored in an elastic object when work is being done to the object
What happens when the work being done to an elastic object stops?
The elastic energy stored within the object is released
Some transferred as kinetic energy
May make the aroma vibrate more so it becomes warmer
What improvements can be made to help with fuel economy?
- reducing the speed
- fitting a wind deflector
- both reduce the air resistance on the vehicle and so reduce fuel use
What does an anti- skid surface do?
They increase the friction between a car tyre and the road surface
How can you work out the extension of a spring from :
1 length after stretching
2 original length
Spring extension = length after stretching - original length
When is work done on an object?
When a force makes it move
Work done = ?
Energy transferred
How can you work out the work done from :
1 the force
2 distance moved in direction of the force
Work done = Force x distance moved in direction of the force
What is gravitational potential energy?
The energy stored in an object because of its position in the Earth’s gravitational field
What does the gravitational potential energy depend on?2
It’s weight and how far up it moves vertically
What is the kinetic energy of an object?
The energy of that an object has due to its motion
What does kinetic energy depend on?2
Mass and speed
What makes an object elastic?
If it regains its shape after being stretched or squashed
What is he unit of momentum?
Kg m/s
What three things happen when two object push apart? 3
- they move apart
- with a different speed if they have unequal masses
- with equal and opposite momentum, so their momentum is zero
What does the force of the impact depend on when two vehicles collide?3
- mass
- change in velocity (speed)
- duration of impact (time)
If the impact time is longer what happens to the impact force?
The longer the time the less impact force
What is the purpose of crumple zones in a car?
They lessen the force of impact by increasing the impact time
What is another way of expressing the effect of an impact on an object?
G-force
What do seat belts do for you?2
They spread the force across the chest
Increase the impact time
What do side impact bars do?
Give way in an impact so increase the impact time
What do we use consecration a of momentum for?
Finding the speed of a car before an impact
What are electromagnetic waves?
Electric and magnetic disturbances that transfer energy from one place to another
What speed does electromagnetic waves travel at?
300 million m/s
What does white light contain?
All colours of the visible spectrum
The warmer the air the…?
Greater the speed of sound
How do anti skid surfaces work?
They increase the friction between the tyre and the road
The surface is rougher and lighter to make it clear
How can fuel economy be improved?
By fitting a wind deflector
Reducing the speed
Reduce air resistance — reduce fuel use
When an elastic object is stretched what energy is stored in the object?
Elastic potential energy
When the stretching force is removed hat happens?
The elastic energy stored is release
Some of it maybe trad feted into kinetic energy to make objects vibrate more and become warmer
How does momentum explain an air bag?
Increased time taken for head to stop
Decreased rate of change in momentum (deceleration)
Reduced force on head
When is work done?
When a force caused an object to move through a distance
What is gravitational potential energy?
The energy that an object has by virtue of its position in a gravitational field
What happens to an objects gravitational potential field strength, when an object is raised?
Work is done against gravitational force
So the object gains gravitational potential energy
What is momentum measured in?
Kg m/s
Examples of the conservation of momentum?
Collisions
Explosions
What is the conservation of momentum?
The total momentum before an event is equal to the total momentum after th event
What does work done depend on?
Size of force
Distance moved
What happens to GPE when an object is moved up?
It’s gravitational potential energy increases
What happens to the GPE when an object moves down?
GPE decreased
Decrease in gravitational potential energy is equal to the work done by the force of gravity acting on it
What does work done when an object moved up or down depend on?
Vertical change in height
It’s weight
Unit of momentum?
Kg m/s
What is effect of the crumple zone?
Increases impact time
So lessens impact force
How do air bags work?
The inflated bag spreads the force of an impact across the upper body of the car
Increases the impact time the effect of the force is lessened
What does a seat belt prevent?
It stops its wearer from continuing forwards when the car suddenly stops
How does a seat belt work?
Decelerating force is reduced by wearing a seat belt
The seat belt acts across the chest so it spreads the force out
Energy transferred is equal to what?
The work done to it
How (in terms of forces) do you lift a box from the ground?
The force you need to lift an object is equal to the opposite force of gravity
So the upward force needed to apply is EQUAL TO THE OBJECTS WEIGHT
What happens to an object when it is moved up?
GPE increase
This increase is equal to the amount of work done
What happens when an object is moved down?
GPE decreases
This decrease is equal to the work done by the force of gravity acting on it
How do kinetic recovery systems work?
They store energy when a vehicle breaks and uses it later eg to boost speed in Formula 1
When a skateboard moves backward, why does the skateboarder move forwards?
Momentum before jumping = momentum after jumping
Before momentum of both is zero
After jumping the skateboarder has momentum forwards so the skateboard must have momentum backwards
